Display device and display method of the same

ABSTRACT

According to one embodiment, when displaying an image on a display panel, projecting an image which is displayed on the display panel, inclining the image which is projected from the display panel at a predetermined angle of bend, and reflecting the image which is projected from the display panel via a prism and guiding the image to a projection surface, a display device corrects input picture image of the prism based on characteristics contrary to the chromatic aberration characteristics of the prism.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2016-115279, filed Jun. 9, 2016, theentire contents of which are incorporated herein by reference.

FIELD

An embodiment described herein relates generally to a display deviceadopting a head-up display mainly for automobile use, and a displaymethod of the same.

BACKGROUND

In general, a display device adopting an automotive-use head-up display(HUD) projects a picture image (virtual image) such as a navigationinstruction and a lane departure warning on the windshield of a vehicleand displays the picture image to be superimposed on the driver's view(real view) ahead of the vehicle. In this way, the driver can check anavigation instruction, a warning and the like without making a largemovement of the eyes or a great adjustment of the focus of the eyes, andthis contributes to an improvement in the safety of the driver.

In the meantime, a display device adopting a recent HUD does not simplydisplay a picture image on the windshield but displays a picture imagesuch that the picture image is superimposed on the driver's view, thatis, on the view of the road ahead of the vehicle at a distance of aboutfour meters. However, since the picture image is always displayed as anupright image, when superimposed on the driver's view with a sense ofdepth such as the view of the road, the picture image may be confusingto the driver in some cases.

As described above, in conventional display devices adopting HUDs, sincea picture image is displayed as an upright image on the windshield,there is a case where the driver finds the picture image confusing withrespect to the driver's view with a sense of depth such as the view ofthe road.

Therefore, the present embodiment aims to provide a display device and adisplay method of the same which can display a picture image on awindshield intelligibly according to a real image with a sense of depth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the general structure of a displaydevice adopting a HUD of an embodiment.

FIG. 2 is an explanatory diagram showing an angle of bend for a prismused in an optical system device of the display shown in FIG. 1.

FIG. 3 is an explanatory diagram showing the definition of the angle ofbend at which an image is formed by the prism shown in FIG. 2.

FIG. 4 is an explanatory diagram showing the dependence on the angle ofincidence of the prism based on the definition of the angle of bendshown in FIG. 3.

FIG. 5 is an explanatory diagram showing chromatic aberration caused bythe prism shown in FIG. 2.

FIGS. 6A, 6B, and 6C are explanatory diagrams showing correction for thechromatic aberration caused by the prism shown in FIG. 5.

FIG. 7 is a diagram showing another arrangement of a backlight withrespect to a display panel of the display device shown in FIG. 1.

FIG. 8 is a diagram showing a structure in a case where only a part(left part) of an image displayed on the panel is inclined by the prismin the display device shown in FIG. 1.

FIGS. 9A, 9B, and 9C are diagrams showing an image displayed on thepanel, an image projected from the panel, and an actual imagesuperimposed on the driver's view in a case where a part of the imagedisplayed on the panel is inclined as shown in FIG. 8.

FIG. 10 is a conceptual diagram showing a structure where the angle ofbend is increased by use of several prisms in the display device shownin FIG. 1.

FIG. 11 is a conceptual diagram showing a structure of the prism wheresmall prisms are formed into a plate in the display device shown in FIG.I.

DETAILED DESCRIPTION

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

According to the embodiments, a display device includes an imageprocessing device and an optical system device. The image processingdevice includes an image generation unit which generates an image whichis to be displayed, an image correction unit which corrects thegenerated image, and an image output unit which outputs the correctedimage. The optical system device includes a display panel which displaysthe image which is output from the image output unit, a backlight sourcewhich projects the image which is displayed on the display panel, aprism which inclines the image which is projected from the display panelat a predetermined angle of bend, and a group of mirrors which reflectsthe image which is projected from the display panel via the prism andguides the image to a projection surface. The image correction unitcorrects the input picture image of the prism based on characteristicscontrary to the chromatic aberration characteristics of the prism. Asfor the output picture image of the prism, chromatic aberration reducedby this.

Further, according to the embodiments, when displaying an image on adisplay panel, projecting the image which is displayed on the displaypanel, inclining the image which is projected from the display panel ata predetermined angle of bend, and reflecting the image which isprojected from the display panel via a prism and guiding the image to areflection surface, the display methods includes correcting the inputpicture image of the prism based on characteristics contrary to thechromatic aberration characteristics of the prism.

According to the above-described structure, the display device canobliquely display the picture image in conformity to the driver's viewsuch as the view of the road.

Embodiments will be described hereinafter with reference to theaccompanying drawings.

First Embodiment

FIG. 1 is a block diagram showing the general structure of a displaydevice adopting a HUD of the first embodiment. The HUD shown in FIG. 1includes an image processing device 11 and an optical system device 12.The image processing device 11 includes an image generation unit 111, acorrection processing unit 112, and an image output unit 113. The imagegeneration unit 111 generates a display image according to a currentlocation which is obtained by a positioning system such as the GPS. Thecorrection processing unit 112 applies chromatic aberration correctionto a part of or a whole image which is generated by the image generationunit 111 as needed. The image output unit 113 outputs an image to whichthe chromatic aberration correction is applied as needed.

The optical system device 12 includes a liquid crystal display (LCD)panel 121, a backlight source 122, a prism 123, a mirror 124, a concavemirror 125, and a reflection film 126. The LCD panel 121 displays animage which is output from the image output unit 113. The backlightsource 122 projects an image which is displayed on the LCD panel 121.The prism 123 is an equilateral triangular prism, and inclines a part ofor a whole projection image of the LCD panel 121 at a predeterminedangle of bend. The mirror 124 reflects in a predetermined direction, animage which is projected from the LCD panel 121 and is inclined by theprism 123 and an image which is projected from the LCD panel 121 and isnot transmitted via the prism 123. The concave mirror 125 enlarges animage which is reflected off the mirror 124 and reflects the enlargedimage in a predetermined direction. The inner side of the windshield ofthe vehicle is coated with the reflection coat film 126, and thereflection film 126 reflects a projection image from the concave mirror125 in the driver's line of sight.

The mirror 124 and the concave mirror 125 secure the distance to theprojection surface such that the projection image can provide the driverwith a sense of depth. Although two mirrors are used in the presentembodiment, the number of mirrors can be increased or reduced dependingon the restriction of the installation place, and the required distance.

In the above-described structure, the angle of bend for the prism 123 iscalculated by the following equations. Here, as shown in FIG. 2, thesection is an equilateral triangle, the refractive index of air is n1,the refractive index of the prism 123 is n2, the angle of incidence onthe prism 123 is θ1, the angle of emergence into the prism 123 is θ2,the angle of incidence on the prism 123 is θ3, the angle of emergencefrom the prism 123 to the outside is θ4.

In this case, the following equation is established:

n1 sin (θ1)=n2 sin(θ2).

According to the above equation, θ2 can be expressed as follows:

θ2=arcsin(n1 sin(θ1)/n2)   (1).

Here, if n1=1 and n2=1.5,

θ2=arcsin(sin(θ1)/1.5).

When e1=60°,

θ2=35.3°.

Therefore, the angle of bend is about 25°.

Similarly, the following equation is established:

n2 sin(θ3)=n1 sin(θ4).

According to the above equation, θ4 can be expressed as follows:

θ4=arcsin(n2 sin(θ3)/n1)   (2).

Here, if n1=1 and n2=1.5,

θ4=arcsin(1.5 sin(θ3)).

When θ2=35.3°,

θ3=180−(120+θ2)=60−θ2=24.7°  (3).

Therefore, θ4=38.8°.

Consequently, the angle of bend α according to θ1 to θ4 is derived asfollows:

α=θ1+θ4−60=38.8°.

Further, according to the above equations (1), (2), and (3), the angleof bend a can be expressed as follows:

α=θ1+θ4−60=θ1+arcsin(n2 sin(60−arcsin(n1 sin(θ1)/n2)/n1)−60.

That is, the prism 123 is arranged with respect to the LCD panel 121 asshown in FIG. 3. According to this arrangement, when the display screenof the LCD panel 121 is viewed via the prism 123, a picture image isdisplayed in the position of an apparent panel which is inclined at theangle of bend α. At this time, as is evident from the dependence of theangle of bend a on the angle of incidence shown in FIG. 4, the angle ofbend α is about 40°.

In the meantime, when the prism is used, chromatic aberration (whichincreases with increasing wavelength) caused by spectral characteristicsof the prism shown in FIG. 5 needs to be taken into consideration.Therefore, in the present embodiment, chromatic aberration correction isapplied to an image which is to be transmitted through the prism 123 bythe correction processing unit 112.

FIGS. 6A, 6B, and 6C show an example of the chromatic aberrationcorrection. In the case of displaying an original image shown in FIG. 6,with respect to RGB color components, the same images are usuallydisplayed in the same pixels. When the original image is viewed throughthe prism 123, since the output angle varies depending on the wavelengthof a color component, chromatic aberration occurs, and the image becomesblurry in the direction of inclination. To prevent the blurriness, asshown in FIG. 6B, the images of the RGB color components are stretchedin the direction of inclination, respectively, according to thewavelengths. At this time, the stretch rate is set to havecharacteristics contrary to the chromatic aberration characteristics ofthe prism, that is, a color with a shorter wavelength (R<G<B) will havea larger aberration. The RGB compound image which has been corrected forthe chromatic aberration is displayed such that the RGB color componentsare misaligned with each other as shown in FIG. 6C, but since thecharacteristics contrary to the chromatic aberration will be neutralizedby the prism 123, the RGB compound image will look the same as theoriginal image when viewed through the prism 123.

From the above, according to the display device adopting the HUD of thepresent embodiment, the display screen of the LCD panel 121 is obliquelyviewed via the prism 123. Therefore, when the image which is displayedon the LCD panel 121 is projected to the reflection surface on thewindshield, the image is inclined in the direction of depth. Here,correction for the chromatic aberration to be caused by the prism 123 ismade to the output of the RGB color components according to therespective wavelengths at a stage where the RGB images are to bedisplayed. Therefore, at a stage where the RGB images are compoundedtogether via the prism 123, the RGB compound image looks the same as theoriginal image and is free from chromatic aberration.

In the following, application examples of the above-described displaydevice will be described.

Second Embodiment

According to the optical system device 12 of the above-describedstructure, since the display image of the LCD panel 121 is obliquelyviewed, the LCD panel 121 does not have to be perpendicularly irradiatedwith the backlight from behind. For example, as shown in FIG. 7, the LCDpanel 121 may be irradiated with the light of the backlight source 121at a predetermined angle from behind. In this case, the best viewingangle characteristics of the LCD can be exhibited in the outputdirection. Therefore, the amount of the output light can be reduced, andthe efficiency of the backlight can be enhanced.

Third Embodiment

If the prism 123 is arranged to cover the entire surface of the LCDpanel 121, since all images are obliquely displayed, some images such asa road sign and a speed limit will be hard to see. Therefore, as shownin FIG. 8, the prism 123 is arranged to cover one part (left half) ofthe LCD panel 121, and the other part (right half) of the LCD panel 121outside the coverage of the prism 123 is directly projected in thepresent embodiment. In this way, an image within the coverage of theprism 123 will be obliquely displayed, while an image outside thecoverage of the prism 123 will not be obliquely displayed but will bevertically displayed.

FIG. 9A shows a display example of the LCD panel 121 in a case where theprism is provided with respect to the left half of the screen as shownin FIG. 8. Here, left images on the display screen, that is, images of atraffic lane and an arrow of a road direction are corrected forchromatic aberration as images to be transmitted through the prism,while right images on the display screen, that is, images of a speedlimit and a current speed are not corrected for chromatic aberrationsince these images will not be transmitted through the prism. In thiscase, as shown in FIG. 9B, the left half images are obliquely displayed,while the right half images are vertically displayed. In this way, asshown in FIG. 9C, the display device can show the driver the trafficlane and the arrow of the road direction on the left side as obliqueimages and the speed limit and the current speed on the right side asvertical images on the driver's view ahead of the vehicle.

Fourth Embodiment

In the above-described embodiment, the angle of bend (angle ofdeviation) is formed between the actual panel position and the apparentpanel position by one prism. However, the arrangement area of the prismis laterally restricted by the viewing angle of the LCD panel, and thusthe angle of bend (angle of deviation) for one prism is limited to about37 to 58°. Therefore, as several prisms (two prisms in FIG. 10) arearranged in combination as shown in FIG. 10, the angle of bend (angle ofdeviation) can be further increased.

Fifth Embodiment

In the above-described embodiment, one equilateral triangular prism isused. However, as shown in FIG. 11, an oblique image may be generated bya plate-like prism where small equilateral triangular prisms areconnected to each other and formed into a plate. In this case, thelength of the light path from the far end of the panel will be shorterthan that of the case of using one equilateral triangular prism, andthis may cause the driver a problem with a sense of perspective.Therefore, the correction processing unit 112 provides an originaldisplay image with perspective in advance. In this way, the displayimage will not cause the driver a problem with a sense of perspective.

As described above, the display device adopting the HUD of the presentembodiment can realize oblique image display with the optical systemwhich is downsized as compared to those of conventional devices.Further, since the oblique virtual image is optically generated, theimage can be naturally displayed. Still further, regarding the chromaticaberration caused by the prism, the chromatic aberration is corrected bythe image processing, costly fluorite will not be required, andconsequently the cost of the optical element can be reduced. Stillfurther, since the prism is arranged with respect to the panel to covernot all but some display images on the panel, oblique images andvertical images can be simultaneously displayed. Still further, althoughthe angle of bend for the prism whose apex angle is 60° is about 37 to58°, the angle of bend can be increased by use of several prisms incombination.

Note that, although the display panel has been assumed to be a liquidcrystal display panel in the above-described embodiments, the displaypanel can similarly be achieved also by an organic EL display panel.

In addition, the invention is not limited to the above-describedembodiments but may be implemented in various other forms withoutdeparting from the spirit of the invention at the stage ofimplementation. Further, various other inventions may be formed byappropriate combinations of the structural elements described in eachembodiment. For example, some of the structural elements described inthe embodiment may be deleted. Still further, the structural elements inthe different embodiments may also be combined with each other asneeded.

1-7. (canceled)
 8. A display device comprising: a display panel whichdisplays an image; a prism which is arranged so that a plane ofincidence inclines at a first predetermined angle with respect to thedisplay panel, inclines the image which is projected from the displaypanel, and outputs the image at a second predetermined angle; a mirrorwhich reflects the image through the prism; and a concave mirror whichreflects the image from the mirror, wherein the image displayed on thedisplay panel is an image obtained by dividing an original image foreach of primary color components, and stretching and synthesizing thedivided image at a stretch rate for each of the primary colorcomponents, respectively, at the stretch rate of each of the primarycolor components set to have characteristics contrary to chromaticaberration characteristics of the prism such that a shorter an image ofa primary color component a larger its wavelength.
 9. The display deviceof claim 8, further comprising a backlight source which projects theimage displayed on the display panel.
 10. The display device of claim 8,wherein the image for each of the primary color components is stretchedin accordance with the angle at which the plane of incidence of theprism inclines with respect to the display panel and a wavelength of theprimary color component.
 11. The display device of claim 9, furthercomprising a windshield which reflects the image from the concavemirror.
 12. The display device of claim 9, wherein the backlight sourceirradiates the display panel from behind at a third predetermined angle.13. The display device of claim 8, wherein the prism inclines one partof the image which is projected from the display panel at the secondpredetermined angle.
 14. The display device of claim 8, furthercomprising a second prism in addition to the prism, wherein the secondpredetermined angle is increased by use of the prism and the secondprism in combination.